In addition, we also made separate maps of the 141 individual sub-bands so that we could test various spectral models for the emission mechanisms at the hotspots. For this, we used the same multi-scale method described above to carry out the deconvolution, which provided a model for the source surface brightness distribution at each sub-band. As we planned to compare the hotspot spectra from LOFAR with those obtained with the VLA at higher frequency, but at a more coarse resolution of 4.5 arcsec [1]}, we restored our clean models with a circular 4.5 arcsec FWHM beam and measured the peak surface brightness at the position of the hotspots for each of the 141 sub-bands. The spectra of the individual sub-bands are presented in Fig. REF , where all 141 spectral data points are plotted. The uncertainties of these data points were determined by adding in quadrature the absolute flux density calibration error of about 2 per cent, which dominates the uncertainty, and the rms noise of the individual maps of each sub-band (typically about 200 mJy beam\(^{-1}\) ).
